The present invention relates to a method and apparatus for providing voice and data communication in a communications system, and particularly for providing voice and data communication using the same transceivers in a base station.
Packet switch technology, which may be connection oriented (e.g., X.25) or xe2x80x9cconnectionlessxe2x80x9d (e.g., the Internet protocol xe2x80x9cIPxe2x80x9d), does not require the set up and tear down of a physical connection, which is in marked contrast to circuit switch technology. This reduces the data latency and increases the efficiency of a channel in handling relatively short, bursty, or interactive transactions. A connectionless packet switch network distributes the routing functions to multiple routing sites, thereby avoiding possible traffic bottlenecks which could occur when using a central switching hub. Data is xe2x80x9cpacketizedxe2x80x9d with the appropriate end-system addressing and then transmitted in independent units along the data path. Intermediate systems, sometimes called xe2x80x9crouters,xe2x80x9d stationed between the communicating end-systems make decisions about the most appropriate route to take on a per packet basis. Routing decisions are based on a number of characteristics, including: least cost route or cost metric; capacity of the link; number of packets waiting for transmission; security requirements for the link; and intermediate system (node) operation status.
Packet transmission along a route that takes into consideration path matrics as opposed to a single circuit set-up, offers application and communication flexibility. It is also how most standard local area networks (LANs) and wide area networks (WANs) have evolved in the corporate environment. Packet switching is appropriate for data communications because many of the applications and devices used, such as keyboard terminals, are interactive and transmit data in bursts. Instead of a channel being idle while a user inputs more data into the terminal or pauses to think about a problem, packet switching interleaves multiple transmissions from several terminals onto the channel. Packet data provides more network robustness due to path independence and the routers ability to select alternative paths in the event of network node failure. Packet switching, therefore, allows for more efficient use of the network lines. Packet technology offers the option of billing the end user based on amount of data transmitted instead of connection time. If the end user""s application has been designated to make efficient use of the air link, the number of packets transmitted will be minimal. If each individual user""s traffic is held to a minimum, then the service provider has effectively increased network capacity.
Packet networks are usually designed and based on industry wide data standards, such as the open system interface (OSI) model or the TCP/IP protocol stack. The standards have been developed, whether formally or defacto for many years, and the applications that use these protocols are readily available. The main objective of standards-based networks is to achieve interconnectivity with other networks. The Internet is todays most obvious example of such a standards-based network pursuant of this goal.
Packet networks, like the Internet, or a corporate LAN, are integral parts of todays business communications environments. As mobile computing becomes pervasive in these environments, wireless service providers such as those using TIA/EIA/IS-136 are best positioned to provide access to these networks. Nevertheless, the data services provided by or proposed for cellular systems are generally based on the circuit switched mode of operation, using a dedicated radio channel for each active mobile user.
A few exceptions to data services for cellular systems is based on the circuit switched mode of operation are described in the following documents, which include the packet data concepts.
U.S. Pat. No. 4,887,265 and xe2x80x9cPacket Switching in Digital Cellular Systems,xe2x80x9d Proc. 38 IEEE Vehicular Technology Conference, pp. 414-418 (June 1988) describe a cellular system providing shared packet data radio channels, each one capable of accommodating multiple data transmissions. A mobile station requesting packet data service is assigned to a particular data packet channel using essentially regular cellular signalling. The system may include packet access points (PAPs) for interfacing with packet data networks. Each packet data radio channel is connected to one particular PAP and is thus capable of multiplexing data transmissions associated with that PAP. Handovers are initiated by the system in a manner that is largely similar to the handover used in the same system for voice channels. A new type of handover is added for those situations when the capacity of a packet channel is insufficient.
These documents are data transmission oriented and based on using system initiated handover in a similar way as for regular voice calls. Applying these principles for providing general purpose packet data services in a TDMA cellular system would result in spectrum inefficiency and performance disadvantages.
U.S. Pat. No. 4,916,691 describes a new packet mode cellular radio system architecture and a new procedure for routing (voice and/or data) packets to a mobile station. Based stations, public switches via trunk interface units, and a cellular control unit are linked together via a WAN. The routing procedure is based on the mobile station initiated handovers and on adding to the header of any packet transmitted from a mobile station (during a call) an identifier of the base station through which the packet passes. In the case of an extended period of time between subsequent user information packets from a mobile station, the mobile station may transmit extra control packets for the purpose of conveying cell location information.
The cellular control unit is primarily involved at call establishment, and it assigns to the call a call control number. It then notifies the mobile station of the call control number and the trunk interface unit of the call control number and the identifier of the initial base station. During a call, packets are then routed directly between the trunk interface unit and the currently serving base station.
The system described in U.S. Pat. No. 4,916,691 is not directly related to the specific problems of provided packet data services in TDMA cellular systems.
xe2x80x9cPacket Radio in GSM,xe2x80x9d European Telecommunications Standards Institute (ETSI) T DOC SMG 4 58/93 (Feb. 12, 1993) and xe2x80x9cA General Packet Radio Service Proposed for GSM, xe2x80x9d presented during a seminar entitled xe2x80x9cGSM in a Future Competitive Environment,xe2x80x9d Helsinki, Finland (Oct. 13, 1993) outline a possible packet access protocol for voice and data in GSM. These documents directly relate to TDMA cellular systems, i.e., GSM, and although they outline a possible organization of an optimized shared packet data channel, they do not deal with the aspects of integrating packet data channels in a total system solution.
xe2x80x9cPacket Data over GSM Network,xe2x80x9d T DOC SMG 1 238/93, ETSI (Sep. 28, 1993) describes a concept of providing packet data service in GSM based on first using regular GSM signalling and authentication to establish a virtual channel between a packet mobile station and an agent handling access to packet data services. With regular signalling modified for fast control set-up and release, regular traffic channels are then used for packet transfer. This document directly relates to TDMA cellular systems, but since the concept is based on using a xe2x80x9cfast switchingxe2x80x9d version of existing GSM traffic channels, it has disadvantages in terms of spectrum efficiency and packet transfer delays (especially for short messages) compared to a concept based on optimized shared packet data channels.
Cellular digital packet data (CDPD) Systems Specification Release 1.0, July, 1993, which is expressly incorporated herein by reference, describes a concept for providing packet data services that utilize available radio channels on current advanced mobile phone service (AMPS) systems, i.e., the North American Analog Cellular System. CDPD is a comprehensive, open specification endorsed by a group of U.S. cellular operators. Items covered include external interfaces, air link interfaces, services, network architecture, network management, and administration. The specified CDPD system is to a large extent based on an infrastructure which is independent of the existing AMPS infrastructure. Commonalities with AMPS systems are limited to utilization of the same type of radio frequency channels and the same base station sites (the base station used by CDPD may be new and CDPD specific) and employment of a signalling interface for coordinating channel assignments between the two systems.
As stated above, a CDPD based radio station is placed beside the AMPS base station. The two base stations use the same antennas. The CDPD transceivers get information from the AMPS system on idle radio frequency channels and tunes its transceivers to those channels. If an RF channel currently used by CDPD is assigned to a cellular phone call, this is detected by the CDPD base station. The CDPD transceiver ramps down its output power and tunes to a new idle RF channel and resumes its transmissions.
One of the problems with the current solution is that it requires extra transceivers to be able to use CDPD at an AMPS site. One extra transceiver is required for each simultaneous CDPD channel required. If, for example, three simultaneous CDPD channels are required at a site, three extra transceivers are required at that base station. Since the CDPD transceivers continuously change radio channels, cavity combiners cannot be used. Currently alternatives are to use a duplex filter and send CDPD on the AMPS receiver antennas or to use hybrid combiners. Duplex filters degrade the received performance of the AMPS base station while hybrid combiners have problems with high output power. Thus, there is a need for a method and apparatus for providing CDPD support in a wireless communication system which overcomes all of the problems cited above.
It is an object of the present invention to overcome the problems cited above with the prior art by providing a method and apparatus so as to allow a CDPD base station to use the transceivers of a cellular mobile radio telephone system to transmit data. The CDPD base station can be designed to take advantage of the cellular system transceivers. When a voice channel goes idle, the transceiver changes mode from voice to packet data on the same radio frequency channel. As a result, no tuning of cavity combiners is required. When the cellular system requires the transceiver again, it will change back to the voice mode. This implies that the CDPD system will use different transceivers for each of these hops. This mode switch of the transceiver can be done within a few milliseconds as required by the CDPD system. The solution can be further enhanced by changing the channel selection algorithm from the cellular system to, preferably, select channels not used by the CDPD system.
According to one embodiment of the present invention, a method for providing support for voice communications and data communications at a base station which has a plurality of transceivers, each having a voice mode of operation and a data mode of operation, is disclosed. A first voice call is assigned to a first transceiver, wherein the mode of the transceiver is set to the voice mode of operation. A data transmission is assigned to a second available transceiver, wherein the mode of the transceiver is set to the data mode of operation. The data transmission is halted when a second voice call needs to be handled by the second transceiver. The mode of operation of the second transceiver is changed from the data mode to the voice mode and the second call is initiated. The data transmission is then assigned to the next available transceiver as long as a voice call does not need to be carried, wherein the mode of the transceiver is set to the data mode of operation.
According to another embodiment of the present invention, a method for providing support for voice communications and data communications at a base station which has a plurality of transceivers, all of said transceivers having a voice mode of operation and a subset of the plurality of transceivers also having a data mode of operation, is disclosed. A first voice call is assigned to a first transceiver, wherein the mode of the transceiver is set to the voice mode of operation. A second voice call is assigned to an available transceiver in said subset of transceivers when the transceivers outside said subset are not available. An intra-cell handover of the second voice call handled by a transceiver in said subset of transceivers is performed to a transceiver outside said subset when the transceiver becomes available so as to make the transceiver in the subset available for a data transmission.